1. Field of the Invention
The present invention relates to a sheet post-processing apparatus and a sheet post-processing method that perform post-processing for a sheet discharged from an image forming apparatus such as a copier, a printer, or a composite device.
2. Description of the Related Art
In recent years, there is developed a sheet post-processing apparatus, which is disposed adjacent to the sheet discharge section of an image forming apparatus main body for the purpose of performing post-processing, such as sorting and stapling, for a sheet on which an image has been formed in the image forming apparatus. The sheet post-processing apparatus performs post-processing for a succeeding sheet after completion of the post-processing for a preceding sheet. In order for the sheet post-processing apparatus to wait until the post-processing for a preceding sheet has been completed, an apparatus in which a retreating path is formed in the middle of a path reaching to a stapler is disclosed in Japanese Patent Publication (Kokoku) No. H6-99070.
However, in the case where the retreating path is formed in the middle of a path reaching to a stapler as described above, the length of a sheet path extending from the discharge section of the image forming apparatus main body to the stapler is increased. This may prevent size reduction of the entire apparatus.
Further, in such a sheet post-processing apparatus, when a plurality of sheets are aligned and bundled to be discharged onto a sheet discharge tray after completion of sheet post-processing, only the lowermost sheet contacting the surface of the sheet discharge tray may be displaced in some cases even though the sheet bundle are discharged in an aligned state. This displacement is caused due to a difference in the friction coefficient between the sheet and surface of the sheet discharge tray. The displacement may adversely affect the sheet alignment performance.
In light of the above, it is desirable to provide a sheet post-processing apparatus capable of reducing the distance between the sheet discharge section of an image forming apparatus and a processing mechanism that performs post-processing to thereby achieve miniaturization of the entire apparatus and enhancing the reliability of the sheet alignment when the sheet bundle is discharged onto the sheet discharge tray.